DIY Stainless Steel Weld Cleaning / Electropolishing


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I love fabrication. Electronics, wood, steel, food, etc. I build stainless steel sculptures and I...

When stainless steel is heated to welding temperatures, it turns lots of pretty colors - gold, red, purple, blue - depending on the temperatures. These look nice, but if you want your stainless steel to look like stainless again, a polishing step is required.

Mechanical polishing using a surface conditioning pad works nicely to remove the color, but has disadvantages - any mechanical polishing will change the surface texture. If you've polished the steel to a different texture before welding, it can be difficult to get the original texture back. Additionally, mechanical polishing requires getting the polisher in what might now be a limited space.

The best way to clean stainless steel without these problems is by electropolishing. Electropolishing works by accelerating an oxidation reaction of an acidic electrolyte on a metal surface using electricity. For the details, you can read the electropolishing wikipedia entry. As a side benefit, cleaning your stainless steel using electropolishing helps it become properly passivated. This means the surface is covered in an iron-free chromium oxide layer. If the surface is not properly passivated, your stainless steel might not be so stainless.

There are some commercial tools out there for electropolishing stainless steel that look really great but are prohibitively expensive, even the cheapest costs nearly as much as the TIG welder I used to make these welds in the first place. Fortunately, it's not hard to do with a standard bench power supply and a little polishing wand that you can either DIY or use some fancy parts.

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Step 1: Power Supply

Any power supply that puts out 30 V / 5 A should be fine. This one I bought on the internet for $70. It's pretty handy having the digital voltage and current display and current limit control.

Step 2: DIY Wand

One end of the power supply connects directly to the workpiece (the piece you're polishing), and the other connects to a wand that you do the polishing with. The wand is made from a metal electrode wrapped in a cloth to keep it from making direct contact with the workpiece. The cloth holds the electrolyte liquid and conducts electricity but prevents arcing.

Here I've made the electrode from a scrap piece of 12ga stainless steel cut into a rectangle. It's important to grind off any pointy corners or sharp edges because those will cause arcing a lot sooner. The electrode is connected to a banana plug to alligator clip cable. I used a high current clip in between the alligator clip and the electrode because it clips to the electrode a little bit more securely, but it's not totally necessary.

The electrode is wrapped in fiberglass tape from the auto parts section of a hardware store. This stuff is cheap and holds up ok. I wrap the electrode with the fiberglass tape and secure the fiberglass with electrical tape. I just use one layer of fiberglass, more than that it is difficult to get much current to flow.

To use this you soak the cloth in electrolyte and touch it to the workpiece with the power connected. The circuit is completed causing electricity to flow and the electropolishing reaction to occur on the workpiece surface.

Step 3: Less DIY Wand

This is a wand made from commercial parts designed for this purpose. It is considerably more expensive for this stuff than for the DIY wand, but it's worth it if you want reliability. The electrode is Walter part number 54B038 and a pack of sponges is Walter part number 54B028. One little plastic ring for holding the sponge to the electrode is included with a pack of sponges, or you can just use a rubber band.

This setup is a lot more resistant to arcing than the DIY wand - the sponge lasts a lot longer than the fiberglass before burning out. It conducts electricity better too, so you can polish faster.

Step 4: Polishing Setup

Here you can see my whole setup.

I built the wand using the red wire, since I think of it as the active thing and the workpiece as ground. However, you want the electrode at negative voltage with respect to the workpiece. Since the power supply only puts out positive voltage, I have swapped the connectors where they plug into the power supply. Don't forget, electrode negative!

The electrolyte I used is Walter Surfox-T. I tried a couple other things that worked okay but this cleaned the fastest. It contains strong phosphoric acid, 30 - 60%, with a pH less than 1 (according to the MSDS). Be careful with it! When working with this stuff I wear a respirator mask, safety glasses, heavy welding jacket to keep it off my clothes, and big rubber gloves. You don't need to use a lot of liquid, so just pour a little into a container you can dip the wand into.

To polish, you clip the ground clip to the work piece, turn on the power supply, dip the wand in the electrolyte, and touch it where you want to polish. I set the power supply to the maximum voltage (30 V) and then tweak the current control to control the reaction speed. Ideally the wand will conduct lots of current and the power supply will have to drop the voltage to reach the current setting you indicate. If you are at 30 V and < 1 A is conducted, it probably means you need a more conductive wand. I like to set the current control around 3 A but it's okay to let it run at 5 A. This process can also make your metal shinier, I like to keep the reaction under control to minimize that effect.

After you're done polishing the acid should be wiped up and then the surface washed with a neutralizer such as Walter Surfox-N. This stuff is much less nasty than the electrolyte, but it's a bit basic with a pH of 12.5 or so. If it's not neutralized the acid will continue to attack your metal, leaving it with a milky texture. After neutralization I like to shine it up with some stainless steel cleaner.

Step 5: Before

Here is a picture of some welded stainless steel before polishing. All of those colors came from the heat.

Step 6: After

Here you can see the piece after polishing. The weld and surrounding area looks like nice shiny stainless steel again.

I also included an after picture from an application of this technique on a sculpture of mine. These small welds hold a sculpture to its baseplate. The stainless steel plate was polished and sanded to a nice uniform matte texture before welding. The piece was electropolished after and the texture was recovered. It would've been impossible to get the polisher in there to clean that weld, and even if I could've it would've changed the texture.

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    22 Discussions

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    Pridbor

    Question 6 months ago

    Could you please tell us the settings you use on the Power Supply. Most are referring to use 12V, is that what you use and what about the Amp Limiting?
    Thanks

    6 answers
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    dandroidPridbor

    Reply 6 months ago

    The power supply I use is limited to 30V or 5A. I set both voltage and amp limiting settings to maximum. Since the resistance of the electrolyte is low, it will put out 5A with an applied voltage of less than 30V. (V = IR, R < 6ohms) As I am polishing, the power supply is putting out 5A the whole time and adjusting the applied voltage if the electrolyte resistance changes.

    If I look and see it is putting out less than 5A I know something isn't right with the process. Or, if I wanted to intentionally slow down the process I could use the amp limiting setting to reduce the limit below 5A. To speed up the process I could get a bigger power supply that could put out more than 5A.

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    Pridbordandroid

    Reply 6 months ago

    I thought that I had sent you a Thank you but I don't see it here?? Either way Thanks for your responses!
    May I ask yet another one namely what gauge wires you are using? I got some rather thin "test wires" which I feel might be a bit too thin for the 10A current, but??
    Thanks again
    Preben

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    Pridbordandroid

    Reply 6 months ago

    I was wondering about the Voltage as most other sources I have encountered on youtube are using 12V either via a Car Battery or a Battery Charger. I assume that you meant that the Voltage is kept constant and the Amperage is varying with the Resistance, that's what a Power supply is supposed to do, set Voltage and forget :-)

    I'm getting a 10A Unit same Brand as yours, I like you bought a TIG Unit and I don't want $2k to go down due to my limited use of Metal Polishing.
    Thanks for your Video and response

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    dandroidPridbor

    Reply 6 months ago

    No, I meant what I said. Since the current being put out is hitting the limit of the supply, it has to drop the voltage. In a normal situation where the current is below the limit of the supply, then the current will adjust with the load resistance and the voltage will stay constant where you set it. But here it can't do that.

    Anyway, using it is very simple. Turn all the knobs all the way up and it'll electropolish as fast as the power supply is able to. Then if you want to limit it for some reason, turn down the current limit. I've also found a good way to control the rate is by the amount of the pad you touch to the metal. The current is spread over the area touching, so if you touch the whole pad the polishing goes slow and if you touch just the corner the polishing goes fast.

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    Pridbordandroid

    Reply 6 months ago

    Didn’t realize that the PS reacted in that manner! Thanks for the tips I should have it shortly and start to make my own experiences.

    What happens when you treat areas outside where the welding took place? I have a sculpture with probably 30 linear feet of welds, and I assume that I will spill the cleaning liquid on areas not welded. Do I need to hurry up and clean it up or how long a stretch can I go before removing the liquid?

    Thanks for your responses

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    dandroidPridbor

    Reply 6 months ago

    For sure, the electrolyte gets all over everything. I'll have the electrode in my right hand and a cloth in my left hand to wipe up the excess as I go. The electrolyte is good for the stainless steel surface but it may leave a sort of "watermarked" look on places that it hits. After electropolishing I'll clean up with neutralizer. Then at the end of fabrication I'll wash the whole thing with the electrolyte again and clean up with neutralizer again. You may or may not feel that's necessary.

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    StigJ4

    11 months ago

    Hi Dandroid. Im so glad for your very detailed describtion. I do a little stainless weld my self and in The near future i will make a el.polish setup like yours.Do you by any chance know an alternative liquid substance for the pacification process instead of the 2 product your describe above ?
    best regards Stig

    1 reply
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    dandroidStigJ4

    Reply 11 months ago

    Hi Stig, I still use Surfox-T whenever I do this process. It's easy to get and works well, though you have to be very careful with it. There are a couple of other liquids sold for this purpose that you can find online, though none that are as easy to get. This website: http://www.electropolishing.com/thepolish/diy-elec... has a couple of DIY recipe suggestions. They might be worth the trouble to save some more money, but it doesn't seem any easier.
    cheers, Dan

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    KhaledS46

    Question 1 year ago on Step 6

    Hello, what type of electrolyte liquid is used? Can it be water and salt? Please put it mote simple. Thanks.

    1 answer
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    dandroidKhaledS46

    Answer 1 year ago

    I use a chemical made by Walter, it is called Surfox-T and you can get it on Amazon. It is very dangerous! It is a strong acid. I have burned holes in my pants and gotten burn marks on my skin from spatter. Walter also makes a pH neutral electropolishing chemical called Surfox-G. I tried that one time and it worked very slowly compared to Surfox-T. I imagine salt water would work but also slowly.

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    JoelÖ53

    1 year ago

    Hello!

    Can someone explaine a little how this process works in theory? What is happening with the material? I have been trying to find some info but can´t find it anywere

    1 reply
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    dandroidJoelÖ53

    Reply 1 year ago

    It's called electropolishing, you can find some good information on the wikipedia page. The chemical process that happens is oxidation of the stainless steel surface.

    Stainless steel is mostly iron and chromium. When iron on the surface oxidizes, the iron oxide dissolves into the acid. When chromium on the surface oxidizes, the chromium oxide stays on the surface and protects the metal. So this process both removes the heat discoloration from the stainless steel surface and leaves the surface protected from future corrosion. A process like this is necessary to ensure that stainless steel is properly stainless.

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    GilL3

    2 years ago

    Sorry for being so late but,

    couldn't you use the actual welder as a power source?

    My welder goes all the way to 1A at, I think, 18-25V..

    Anyway, very good work! Like giving it to the MAN..

    2 replies
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    dandroidGilL3

    Reply 2 years ago

    Yeah, you can, the TIG welder I made those welds with puts out way more current than the little power supply I use for electropolishing. However, my TIG welder cost me around $2500 and why risk damaging it doing something kind of off-label. I feel a lot better just using the cheap power supply.

    While I was sorting out the process I tried using a cheap harbor freight welder for the power supply, but the power supply I ended up deciding on was both cheaper and worked better.

    I still do this process all the time, by the way.

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    GilL3dandroid

    Reply 2 years ago

    You've got a good point there, my welder did not cost anywhere near,

    but it stil cost more then a power supply ;-)

    Thanks, gil.

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    petercd

    2 years ago

    A nice upgrade would be a carbon fiber brush, I had the idea of using a 50mm length of CF braided tube crimped in a copper ferrule.

    Just unravel the free end of the braid to form the brush.

    Adding some glycerine to the mix should render it more gel like so that you can glop it around the part instead of it being runny like water.

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    petercdpetercd

    Reply 2 years ago

    A 10mm lug, crimped with a brake tube flaring kit using the 8mm position of the tube holding bars, squeezed in a vise.

    Still needs some heat shrink to avoid direct metal to metal contact.

    cf brush.JPG
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    retropol

    3 years ago

    Great job, well done. There is a commercial product now available at a very affordable price though - its called Retropol. You can read more about it here:

    www.retropol.com.au

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    andyddog

    3 years ago

    Very nice! I have seen one used at a welding seminar and was told it was expensive. I did not realize how simple the tool is. I am going to have to start collecting parts now :)